This application claims priority to an application entitled xe2x80x9cAmplifying Apparatus for a Mobile Station Receiver and Method for Controlling the Samexe2x80x9d filed in the Korean Industrial Property Office on Dec. 29, 1999 and assigned Serial No. 99-65240, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to a mobile station, and in particular, to an amplifying apparatus for securing a good impedance match of a mobile station receiver and a method for controlling the same.
2. Description of the Related Art
FIG. 1 is a circuit diagram illustrating a conventional amplifying apparatus.
Referring to FIG. 1, a CDMA (Code Division Multiple Access) mobile station receives a radio signal through an antenna 110 and provides the received signal to a receiver through a duplexer 109. In the receiver, the received signal is provided to a low-noise amplifier (LNA) 108 through capacitors 107 and 108. The low-noise amplifier 108 amplifies the received signal and provides the amplified signal to a controller (not shown). When the signal output from the low-noise amplifier 108 is higher than or equal to a predetermined level, the controller generates a control voltage Vcont of a first level (e.g., 3V) to attenuate (or decrease) the level of the received signal.
The control voltage Vcont generated by the controller is provided to a base of a bipolar junction transistor (BJT) 111. The BJT 111 is turned ON in response to the control voltage Vcont at the first level. Then, the power supply voltage VCC is provided to a diode 101 in the receiver through resistors 102 and 103. As a result, the diode 101 becomes conductive (or is turned ON), so that the received signal being provided from the duplexer 109 to the receiver is attenuated by the circuit comprised of the resistor 102, the capacitor 105 and the resistor 103.
However, as the diode 101 is turned ON, an impedance of the amplifying apparatus is decreased as compared with the case where the diode 101 is turned OFF. As a result, the impedance of the amplifying apparatus is not matched with an output impedance of the low-noise amplifier 108. Hence, the filtering characteristics of a filter in the receiver is degraded due to the signal output from the low-noise amplifier 108. Further, because of the impedance mismatch, abnormal oscillation occurs and the output signal includes ripple components, so that the demodulated signal may have errors.
It is, therefore, an object of the present invention to provide an amplifying apparatus for securing a good impedance match of a mobile station receiver and a method for controlling the same.
It is another object of the present invention to provide an amplifying apparatus for removing ripple components from the output signal.
To achieve the above and other objects, there is provided an amplifying apparatus for a mobile station receiver. In the amplifying apparatus, a low-noise amplifier amplifies a received signal to a preset level. A controller detects a level of a signal corresponding to a first frame of the received signal output from the low-noise amplifier, and generates a control voltage according to the detected level. An attenuation determining resistor determines an attenuation of the received signal. A first switching element is connected in series to the attenuation determining resistor, and is turned ON according to the control voltage so as to attenuate the received signal through the attenuation determining resistor. An impedance compensation resistor is connected in parallel to the attenuation determining resistor, and compensates for a decrease in an impedance due to turn-ON of the first switching element.
Further, a second switching element is connected in parallel to the impedance compensation resistor and the first switching element. The second switching element is turned ON according to the control voltage so as to provide the received signal to the low-noise amplifier without attenuation.
Preferably, the control voltage is at a first level when the level of the signal corresponding to the first frame of the received signal output through the low-noise amplifier is higher than or equal to a threshold level. The control voltage is at a second level when the level of the signal corresponding to the first frame is lower than the threshold level.
Preferably, when the control voltage is at the first level, the first switching element is turned ON and the second switching element is turned OFF. When the control voltage is at the second level, the first switching element is turned OFF and the second switching element is turned ON.